Pipe runs for sewage systems and the like are terminated at predetermined intervals within manhole assemblies to facilitate maintenance, inspection and repair. A coupling seal is provided between the manhole opening and the pipe to provide a watertight seal therebetween and preferably to allow for some movement of the pipe relative to the manhole assembly, typically caused by external forces.
One technique for accomplishing this type of seal is described in U.S. Pat. Nos. 3,796,406; 3,813,107 and 3,832,438, assigned to the assignee of the present invention. This technique employs a gasket which has its outer periphery embedded in the concrete material during the time that the manhole member is cast. Although this type of gasket provides a good watertight seal between the manhole opening and pipe, the amount of movement which the pipe can experience relative to the manhole opening is quite limited, due to the nature of the gasket. Also, there are a number of applications wherein the gasket is inserted in situ.
The misalignment of a pipe relative to the manhole opening may be significant in certain applications and further since the pipe may undergo a significant amount of movement relative to the manhole as a result of subterranean influences, a gasket has been developed to accomodate significant changes in the displacement between the pipe and the manhole opening, which gasket and method of assembly is described in U.S. Pat. No. 4,103,901, issued Aug. 1, 1978 and assigned to the assignee of the present invention. The gasket disclosed in the last-mentioned patent is comprised of an outer peripheral flange which is embedded in the concrete material from which the manhole assembly is cast. The gasket is provided with a central opening defined by a gasket inner annular periphery shaped to have an appearance substantially similar to an O-ring, said gasket further including an integral, intermediate section having first and second diagonally aligned portions integrally joined at opposite ends to said outer flange and said inner periphery and integrally joined to one another along an imaginary circular line defining a V-shape with the fold being at the point joining the aforesaid portions. The gasket is arranged within the manhole opening such that the outer flange is embedded in the concrete surrounding said opening. The O-ring shaped inner periphery is sufficiently yieldable to embrace the outer surface of a pipe section extending therethrough. The intermediate section of the gasket is generally V-shaped to enable the gasket to resiliently support a pipe, ideally so that its longitudinal axis coincides with the axis of the manhole opening and yet which is sufficiently and readily yieldable to resiliently support the pipe relative to the manhole member and retain the watertight seal therebetween in spite of the fact that the pipe undergoes a significant displacement from the aforementioned concentric position within the manhole opening. This displacement may be of the order of several inches.
Although the above described gasket has the capability of accommodating pipes having an outer diameter which deviates from a nominal value over a significant range which is of the order of several inches and is further capable of maintaining a watertight seal between the pipe and the manhole opening in spite of an alignment displacement therebetween of the order of several inches, the above described gasket is designed to be embedded into the manhole base at the time that the base member is cast.
Many manhole bases, however, are cast independently of the sealing gasket. For example, some manhole bases are cast with no manhole openings or are cast with a smooth manhole opening, defined only by the cast material and having no sealing gasket.
U.S. Pat. No. 4,387,900 issued June 14, 1983 and assigned to the assignee of the present invention describes apparatus which provides all of the capabilities of the above mentioned sealing gasket and which is further capable of being installed in situ. The gasket assembly of U.S. Pat. No. 4,387,900 comprises a gasket member adapted to be fully contained within the manhole opening and comprises an annular outer flange substantially conforming to the size and shape of the manhole opening and initially loosely positioned therein. The gasket is provided with a smaller diameter central opening defined by an inner peripheral edge having an enlarged beaded cross-section, substantially conforming to an O-ring. An intergral, intermediate, generally V-shaped section is arranged between the outer flange and inner beaded periphery and includes two diagonally aligned annular portions integrally joined to one another along an imaginary annular fold line, said intermediate V-shaped section being yieldable and enhancing the ability of the gasket inner periphery, whose central axis normally coincides with the central axis of the outer flange, to be displaced therefrom by a significant displacement distance in order to position and support a pipe within the manhole opening to retain the integrity of the watertight seal therebetween in spite of the fact that the longitudinal axis of the pipe is displaced from the central axis of the manhole opening due to misalignment therebetween which may occur during initial installation or as a result of external influences acting upon the pipe.
The flange of the gasket is secured within the manhole opening by means of a circular compression or clamping band formed of a material which is impervious to corrosive type influences and is installed by means of an expansion assembly comprised of an annular shaped metal band having a discontinuity about its periphery to enable the band to be easily expanded. An hydraulically operated jack is pivotally coupled to the expandable band. The gasket clamping band is placed about the outer periphery of the expandable band, and these members are placed within the interior periphery of the gasket outer flange. The hydraulic jack is pressurized to expand the expandable band which in turn exerts an expansion force which is distributed substantially uniformly about the entire interior periphery of the clamping band, causing the clamping band to be expanded outwardly against the gasket outer flange whereupon the outer periphery of the flange is firmly pressed into intimate engagement with the manhole opening and the flange itself undergoes compression by the clamping band.
Expansion is complete when the hinged segment forming part of the clamping band fits into the gap between the ends of the clamping band. This gap length is predetermined for each standard hole size and assures the proper compression for watertightness. Other prior art techniques employ a pressure gauge for determining when compression is adequate for watertightness. The compression ring of the present invention is molded to exact size and utilizes the installation method described hereinabove.
The clamping band is also provided with a discontinuity to enable the clamping band to be expanded, and is further provided with a short, insertable segment defining one end of the discontinuity and which is hingedly connected to the major portion of the clamping band, preferably by a thin web of the clamping band material. The hinged connection is typically created by forming a cut or recess through the clamping band. The compression ring is preferably molded to exact size and includes a thin flexible section integrally joining the band and the segment to serve as a hinge located a spaced distance inward from one end of the discontinuity. The recess defining one side of the segment is of a depth sufficient to provide a thin web of material sufficient to create a hinged connection between the segment and the major body portion of the clamping band, enabling the segment to be swung away from the opposite end of the band defining said discontinuity in order to facilitate and simplify the loose positioning of the clamping band against the interior surface of the gasket outer flange.
The hydraulic jack is pressurized to expand the expandable metal band. When the gasket flange has been sufficiently compressed against the manhole opening, the insertable segment is swung up into the gap region formed by the discontinuity. Thereafter, the hydraulic pressure is relieved causing the compressed gasket flange to exert a counteracting force against the clamping band which, together with the insertable segment, serves to retain the clamping band in the locked position. The force exerted by the clamping band upon the compressed gasket flange creates and maintains a watertight seal between the outer flange of the gasket and the manhole opening.
The end of the pipe to be arranged within the manhole opening is pressed into the central opening of the gasket. The pipe opening O-ring shaped periphery has an unexpanded inner diameter which is less than the outer diameter of the pipe being pressed into the gasket. The O-ring shaped periphery is capable of expanding to accept the pipe and yet is of sufficient cross-section to exert a substantial holding force upon the pipe. In order to further enhance the watertight seal between the pipe and the gasket, an adjustable tension strap is positioned about the intermediate section of the gasket adjacent said O-ring periphery and is tightened to compress the portion of the gasket immediately adjacent the O-ring periphery firmly about the outer surface of the pipe to assure a watertight seal therebetween.
The gasket serves as a barrier, separating the clamping band and adjustable strap from the exterior of the manhole to shield the clamping band and the strap from external influences, to protect and perserve their useful operating life and to facilitate and simplify maintenance, inspection, repair and replacement thereof from the interior of the manhole assembly.
The clamping assembly of U.S. Pat. No. 4,387,900 has a disadvantage of imparting an expansion force indirectly to the clamping band through the frictional engagement between the expansion band and the clamping band. In addition, the hinged segment of the clamping band may easily be separated from the major portion of the clamping band thus rendering the clamping band ineffective and unusable.
The gasket design utilizing U.S. Pat. No. 4,387,900 further serves an impediment to the insertion, expansion and final clamping placement of the clamping band, thus complicating the operation. Also, the clamping band may become laterally displaced during expansion.